Avoiding groundwater contamination from agricultural activities is possible only if the processes that control deep percolation are understood. The source of contaminant movement to groundwater is typically through preferential flow, processes by which the bulk soil is bypassed by some part of the infiltrating water. Three mechanisms give rise to preferential flow: fingered flow, funnel flow, and macropore flow. Fingered flow occurs in coarse-textured soils and can be minimized by starting with an initially well-wetted profile. Funnel flow is likely in layered soil profiles of silt or coarser-textured soil, in which avoiding slow overirrigation is critical. Macropore flow is observed in all structured soils in which maintaining irrigation rates well below the saturated conductivity of the soil is essential. These prescriptions are quite different than conventional recommendations, which fail to consider groundwater protection.
Amir M. González-Delgado, Manoj K. Shukla and Brian Schutte
( Beven and Germann, 1982 ; Kramer and Boyer, 1995 ). Several studies have reported deeper than expected herbicide leaching through preferential flow channels ( Flury et al., 1995 ; Rao et al., 1974 ; Shukla, 2014 ). The correct use of agrochemicals
Amir M. González-Delgado and Manoj K. Shukla
and water in the soil under field conditions is influenced by macropores that promote their preferential flow ( Beven and Germann, 1982 ; Shipitalo et al., 2000 ). Preferential flow channels in the porous media could enhance herbicide movement from
Ian A. Merwin, John A. Ray, Tammo S. Steenhuis and Jan Boll
Commercial apple (Malus domestica Borkh.) orchards in the northeastern United States receive heavy pesticide inputs and are often located on well-drained soils near surface and groundwater resources. Nonpoint-source water pollution by agrichemicals has been monitored in agronomic crop systems and simulated using computer models and laboratory soil columns, but inadequately studied at field scale in orchards. We monitored the concentrations of agrichemical tracers, nitrate-N, and benomyl fungicide in water samples from two apple orchards under mowed sodgrass (Mowed-Sod), shredded bark mulch (Bark-Mulch), preemergence residual herbicides (Resid-Herb), and postemergence herbicide (Post-Herb) groundcover management systems (GMSs). In one orchard, we evaluated subsurface spatial patterns and flow rates of a weakly adsorbed blue dye (pesticide analog) and potassium bromide (nitrate analog) under trees after six years of Post-Herb and Mowed-Sod treatments. Nitrate and pesticide tracers leached more rapidly and in higher concentrations under Post-Herb treatments, apparently via preferential macropore flowpaths such as root channels, soil cracks, and macrofauna burrows. At another orchard, we monitored subsurface leaching and surface runoff of benomyl and nitrate-N on a whole-field scale. Peak concentrations of benomyl (up to 29 mg·liter-1) and nitrates (up to 20 mg·liter-1) were observed in subsoil leachate under Resid-Herb plots during 1993. In 1994, nitrate concentrations were greater in leachate from all GMSs, with upper ranges from 48 to 66 mg·liter-1, while benomyl concentrations were lower in all GMSs compared with the previous summer. In surface water runoff during 1993, the highest benomyl concentrations (387 mg·liter-1) and most frequent outflows occurred in Resid-Herb plots. During 1994, benomyl runoff was more frequent in both herbicide GMSs, with concentrations up to 61 mg·liter-1 observed in the Post-Herb plots. Weather patterns, irrigation intensity, differing soil conditions under each GMS, and the turfgrass/clover drive lanes affected the relative frequency and concentrations of benomyl and nitrate leaching and runoff. Preferential bypass flow appeared to be a major subsurface leaching pathway, and erosion sediment an important factor in surface movement of these agrichemicals. Our studies suggest that nitrate-N and benomyl fungicide may be more prone to leaching or runoff from orchard soils under some herbicide GMSs in comparison with mowed sodgrass or biomass mulch systems.
Carrot (Daucus carota L.) root shreds were stored under a continuous flow of 0.5% and 2% O2 (balance N2) or air at 5 °C to investigate the effect of low O2 atmosphere on respiratory metabolism, particularly on lactate dehydrogenase (LDH) activity and its isozyme composition. Low O2 atmospheres caused a decrease in CO2 production and an increase in lactate concentration and LDH activity compared to air. By day 2, CO2 production rate decreased 0.4- and 0.5-fold, lactate increased 3.5- and 2.2-fold, and LDH activity increased 2.3- and 1.7-fold in carrot shreds stored in 0.5% and 2% O2, respectively, compared to samples in air. Based on nondenaturing electrophoresis, LDH isozyme composition analysis revealed five bands consisting of a tetrameric enzyme with subunits encoded by two different Ldh genes. Changes in staining intensity of the isozymes indicated that the increase in LDH activity in carrots under low O2 atmospheres resulted from increased enzyme synthesis and that there was preferential induction of one Ldh gene. These results suggest that lactic acid fermentation may be accelerated more under 0.5% than 2% O2 atmospheres due to greater expression of the Ldh genes.
Karine Fouldrin, Anis Limami and Thierry Lamaze
During forcing, the witloof chicory taproot produces an etiolated bud, the chicon. The axis of this organ often is brown as a consequence of a disorder associated with a localized Ca deficiency. The effect of the main anions (NO3 -, Cl-, SO4 2) in the nutrient solution on Ca (45Ca) absorption and translocation in the chicon was investigated. Although the amount of Ca that accumulated in the chicon was not affected by nutrient solution composition, Ca (45Ca) mobility was modified. The amount of radioactivity in the chicon increased slightly when the main anion in the solution was sulfate and decreased markedly when the main anion was chloride, compared to nitrate. Calculations of the specific radioactivity of Ca reaching the chicon and in root tissue suggest that, when slowed down, Ca transport consists of a homogeneous flow in all root tissues, whereas, in other cases, Ca moves along a preferential pathway, such as the xylem vessels. Modifying the anionic composition of the nutrient solution to avoid a localized Ca deficiency is discussed.
Ian A. Merwin, Tammo S. Steenhuis and John A. Ray
Non-point source water pollution by agrichemicals is a recognized problem that has been studied in agronomic crop systems, and simulated using computer models or artificial soil columns, but rarely measured at field scale in orchards. For three growing seasons, we monitored the movement of nitrate and pesticide analogs and a widely used fungicide (benomyl) in two apple orchards under four different groundcover management systems (GMSs), including turfgrass, wood-chip mulch, residual pre-emergence herbicides, and post-emergence herbicide treatments. In subsoil lysimeter samplers at one orchard, we observed that nitrate and pesticide analogs leached more rapidly and in higher concentrations under herbicide plots compared with turfgrass plots. At another orchard where subsoil leaching and surface runoff of benomyl and nitrate-N were monitored in replicated GMS plots, we observed higher concentrations of benomyl (up to 30 μg·liter–1) and nitrate-N up to 50 μg·liter–1) leaching under herbicide GMS. The highest benomyl concentrations (375 μg·liter–1) and most frequent runoff of this pesticide were observed in the residual pre-emergence herbicide plots. Yearly weather patterns, irrigation, and development of different soil physical conditions under the four GMSs determined the relative magnitude and frequency of agrichemical leaching and runoff in both orchards. The agrichemicals apparently leached by mass flow in preferential flowpaths such as old root channels and soil cracks, while surface chemical runoff occurred mostly adsorbed on eroding soil sediment. These observations indicate that orchard GMSs can have a significant impact on leaching and runoff of pesticides and nutrients.
Tyler C. Hoskins, James S. Owen Jr. and Alex X. Niemiera
(i.e., more evenly) in treatments containing a wheat plant than a fallow column. They postulated that roots grew into large pore spaces and effectively created a homogenous pore size distribution that reduced the preferential flow of water through
Ryan N. Contreras, Ron Determann and Mara Friddle
-cedar cultivars. Table 1. Source and relative genome size of Cryptomeria japonica taxa based on flow cytometry of 4′,6-diamidino-2-phenylindole-stained nuclei using Pisum sativum ‘Ctirad’ (2C = 8.76 pg) as an internal standard. Flow cytometry. Approximately
Hamidou F. Sakhanokho and Nurul Islam-Faridi
about the genetics of C. obcordata . For this reason, we decided to determine the chromosome number using a modern protoplast technique to spread root tip chromosomes, nuclear DNA content and base composition using flow cytometry, and the location of